Project Summary/Abstract Young people at highest risk for HIV in the U.S. will be gay, bisexual transgender youth (GBTY) and homeless youth (HY) in communities with high HIV incidence and overwhelmingly Black and Latino. Focusing on Los Angeles and New Orleans, seronegative youth at highest risk for HIV will be screened in homeless shelters and gay-identified community-based organizations (CBO). A cohort of 1500 seronegative youth will be recruited that is 82% male (79% GBTY), 66% Black, 16% Latino, and 18% white, non-Hispanic. About 27% will be 12-17 and 73% between 18-24 years old. All youth will be followed longitudinally over 24 months at four month intervals and tested for HIV, STI, serious substance abuse, health care utilization, and comorbid conditions ? a Prototypical Retention/Prevention (R/P) Strategy. Over 24 months, acutely HIV infected youth will be triaged to Study 1. This Prototypical R/P Strategy operationalizes the CDC's recommendations for the engagement of GBTY in repeat HIV testing, linkage to care, and options for combination prevention (PrEP, PEP ? with behavioral interventions). Building on this team's extensive experience with behavioral and mobile/social media interventions, a randomized controlled trial (RCT) will be conducted with four intervention conditions: 1) an Automated Messaging and Monitoring Intervention (AMMI), which will use texts to diffuse prevention messages daily and to monitor risk behaviors weekly (n=900); 2) a Peer Support intervention on a social media platform (i.e., Facebook) in which young people will post messages and stories about their experiences preventing HIV, plus the AMMI (n=200); 3) an eNavigator intervention in which a B.A.-level staff supports youth, primarily through texting and social media, but also in-person meetings, to provide support in crisis situations, refer to treatment, and assist in gaining access to health care and other services, plus Peer Support and AMMI (n=200); and, 4) a combined intervention of eNavigator, Peer Support, and AMMI (n=200). A single outcome will be composed of six key behaviors (access to medical care, accessing and adherence to PrEP or PEP, treatment of all STI, and 100% condom use). In addition to evaluating the added benefit of increasing levels of intervention, the brief 7- item weekly text-messaging monitoring surveys will provide approximately 100,000 weekly reports of indicators of primary and secondary outcomes that can inform our understandings about the relationships between risk and comorbid states. This study will have policy implications for the allocation of resources to HIV testing resources in local communities, the uptake and scalability of text and social media interventions, and the models for diffusing evidence-based interventions (EBI) globally (without requiring replication with fidelity to a manual).